The present invention relates to a device for intermingling, relaxing, and/or thermosetting of filament yarn in a melt spinning process, as well as associated processes.
During the melt spinning of filament yarns, a melt-spinnable polymer is melted and, in this state, is extruded through fine nozzle orifices of a spinneret plate. This results in a number of melt strands, which are solidified by cooling in an air stream, and are drawn out over a number of rollers with increasing surface speed to form fine filaments. These are then merged to form a unitary yarn, and are finally wound up as bobbins.
The drawing of the filaments is effected on the one hand, provided they are not yet solidified and the polymer has not yet fully crystallised out and is still somewhat capable of flowing, in the area of the cooling way upstream of the first godet roller. This is also referred to as spin drawing. On the other hand, the filaments, after solidifying, are mostly mechanically drawn, as a result of which an orientation effect of the macromolecules of the polymer is achieved, and the definitive expansion and strength values of the yarn are set.
The ratio between spin drawing and mechanical drawing is dependent on the spinning speed. The lower the spinning speed, the higher the degree of mechanical drawing required to obtain what is referred to as fully-drawn yarn. The draw ratio can in this situation be up to 1:4. At medium to low operating speeds (depending on the polymer used, for example, up to about 50 m/s), it may therefore be necessary for the filaments in the area of the drawing zone to be heated up to a temperature above the glass transition point of the second order, in order to facilitate drawing. At high spinning speeds (depending on the polymer used, for example, above about 85 m/s), the draw ratio is substantially smaller, and typically amounts to only about 1:1.3, as a result of which such additional heat treatment can be done away with.
After the extrusion, i.e. the spin drawing and/or drawing, there remain internal tensions in the filaments, which impair the form stability of the yarn, and may lead to the yarn being shortened as tension builds up on the bobbin, with the result that, as a minimum, it becomes impossible to continue winding without some intervention. The forces which arise in this situation may even lead to the destruction of the bobbin tubes. In order to avoid this disadvantageous effect, the yarn is in most cases, after drawing has been carried out, subjected to a repeat heat treatment, by means of which, among other things, it is already shortened before winding, an effect referred to as relaxation shrinkage.
Each filament yarn is also inclined to shorten still further, if subjected after manufacture to higher temperatures of, for example, 100xc2x0 C. or more. This tendency towards longitudinal contraction is referred to, depending on the temperature treatment, as shrinkage at the boil (water 95xc2x0 C.-100xc2x0 C.) or hot-air shrinkage (hot air 160xc2x0 C.-200xc2x0 C.), in which situation downstream industry will only tolerate yarn of which the shrinkage values are within certain limits, e.g. shrinkage at the boil between 6% and 11%. This procedure, referred to as thermal shrinkage can also be reduced by heat treatment of the yarn after drawing, designated hereinafter as thermosetting. Compared with relaxation, however, in this case the attainment of a higher temperature and/or longer period of treatment is required. It has also been shown that, by increasing the spinning speed, the orientation of the macromolecules can be increased in such a way that the yarn will already feature conventional commercial thermal shrinkage values without additional thermosetting. In such a case, relaxation is sufficient to achieve adequate longitudinal stability of the yarn on the bobbin.
In order to improve the cohesion of the individual filaments in the yarn, and therefore improving what is referred to as the thread cohesion, the filaments are frequently also provided with a thread cohesion medium and/or entangled, with the intermingling being carried out as the final stage before winding, but in any event after drawing has been carried out. A distinction needs to be drawn between this and what is referred to as pre-intermingling before drawing. This treatment serves only to provide even distribution of the spin finish preparation on the thread, and a certain degree of cohesion of the filaments, in order in this way to suppress the separation and breakage of individual filaments during the subsequent drawing process. The larger part of the pre-intermingling process applied is nullified again by the drawing process.
Known in the prior art are processes and devices for intermingling, relaxation, and thermosetting, although these are not capable of use, or at least are not effective, in respect of all three types of processing, simultaneously or alternatively, and, in addition, are characterised in terms of apparatus by being either elaborate or expensive, and/or by high consumption of energy or treatment gas.
In the case of yarns produced at low to medium spinning speeds, the prior art allows for control of the thermal shrinkage values to be achieved by the fact that the threads are subjected, after drawing, to adjustable heat treatment by means of heated drawing godets.
As already mentioned, increasing the spinning speed allows for the orientation of the macromolecules in the thread to be increased in such a way that the yarn also features a commercially conventional thermal shrinkage after drawing, even without heat treatment. In this case, only relaxation of the yarn is required in order to avoid shrinkage of the yarn on the bobbin and damage to it. CH 623 611 describes such a process, whereby the yarn is guided through one or more steam jets after drawing by means of unheated godets, the steam emerging from apertures in a treatment chamber open to the side, arranged approximately at right angles to the yarn. The steam nozzles are fed with an overpressure of some 1.7 bar (g), but the steam relaxes to atmospheric pressure almost entirely on emergence from the nozzles, with the result that the yarn may be said to be processed at atmospheric pressure. Accordingly, the maximum steam processing temperatures for the yarn which can be achieved are only about 105xc2x0 C. In addition to relaxation, during this process intermingling of the individual filaments of the yarn also takes place.
U.S. Pat. No. 5,750,215 and U.S. Pat. No. 5,558,826 describe in similar fashion a relaxation process and intermingling with steam, with mentioned also being made of thermosetting adjustment. In this case, too, according to the description, the yarn is treated under atmospheric pressure. Before winding, however, there is still a certain distance of 2-3 m for the yarn to run after the steam treatment, during which the yarn may undergo additional relaxation (due to xe2x80x9claggingxe2x80x9d). It may therefore be doubted whether the steam treatment described is sufficiently effective on its own. In addition to this, a comparable first steam processing of the yarn to determine the drawing point is carried out as early as in the drawing zone between two pairs of godets, which may likewise lead to the impairment of the effect of the second steam treatment. The prognostications for the determination of the drawing point are, incidentally, in contradiction to DE 2204397, in which reference is made to the fact that, as from 3000 m/min, it is no longer possible to set a defined drawing point, and this accordingly need not, or cannot, be monitored any longer.
A further device is described in WO 98/23797, in which several threads are conducted through a steam chamber at atmospheric pressure before being wound up. In the chamber the steam does not impinge on the threads directly, and is released to the outside through lateral apertures. Only relaxation is achieved, and no provision is made for thermosetting or intermingling.
U.S. Pat No. 5,634,249, and EP 0 703 306 which corresponds to it, describes a intermingling effect in a warping process by means of steam, although this relates to the treatment of a yarn already manufactured in a first operational stage, and only partially orientated. The operating speeds, at 584 and 800 m/min respectively, are correspondingly low. In view of the fact that, in the proposed procedure, intermingling is carried out simultaneously and at the same location as the drawing, it is not understandable as to how effective intermingling can take place at all with the high drawn filament tensions which prevail in this situation.
DE 19546784 describes a type of steam chamber for relaxing heat treatment of filament yarn, which makes use of a very special design of nozzle geometry, and by means of which dynamically favourable conditions are intended to be obtained for a complete condensation of the steam and, as a result of this, good thermal transfer to the yarn. The yarn in this situation moves in part through the same nozzle apertures through which the steam flows. Provision is made for a separate intermingling chamber in the intake area of the device, in which a steam jet is imposed onto the yarn from the side.
Use is also made of a technique of conducting the yarn through a chamber subjected to hot steam, in order to heat the yarn for the purpose of facilitating the drawing, in particular at low to medium operating speeds. Corresponding devices are known, for example, from U.S. Pat. No. 5,487,860, DE 2643787, DE 2204397, or DE 33 46 677.
The object on which the present invention is based is to provide a device capable of universal application for melt spinning of the type referred to in the preamble, and corresponding processes, by means of which the yarn, as required, is relaxed, entangled, and by means of which a thermoshrinkage adjustment can also be effectively carried out. In addition, the device should also be of simple design and economical in operation. This object is resolved according to the invention by a device with the features of Patent claim 1, as well as by the processes described in claims 13 and 14. Advantageous embodiments and further developments are characterised in the sub-claims.
The device according to the invention comprises a treatment chamber, which is capable of being filled with a gas under an essentially static over-pressure and elevated temperature, and an intake and outlet aperture for the passage of the yarn, which is gas permeable under pressure release, and through which, accordingly, the gas can flow out under pressure release, and in respective contrary to the direction of run of the yarn.
The device according to the invention accordingly no longer, quite particularly, includes any nozzle through which a jet of the processing gas might be directed onto the yarn for the purpose of intermingling it essentially transverse to its direction of run. Rather, the device according to the invention results in a intermingling of the yarn or its filaments on their passing through the intake and/or outlet aperture of the treatment chamber, due to the gas emerging through these apertures with pressure release in or contrary to the direction of run of the yarn.
The intermingling effect which occurs in this situation is surprising, since previous opinion was that the highest intermingling effect is achieved with an impact angle of the gas onto the yarn of 90xc2x0, and it was known that, as the angle decreased, the intermingling is largely reduced in proportion. At values of close on 0xc2x0, accordingly, practically no more intermingling was to be expected. However, with the device according to the invention, intermingling nevertheless still occurs, and specifically due to the fact that the yarn is passed through (at least) one intermingling nozzle itself (in the form of the intake and/or outlet aperture of the treatment chamber).
With conventional intermingling nozzles, the intermingling rate attained is directly dependent on the gas pressure applied, and therefore on the thrust with which the gas jet imposes on the yarn. The intermingling achieved by the device according to the invention is, by contrast, relatively independent of the gas pressure applied, and exceeds in its level even that of conventional intermingling processes.
The intermingling of the yarn which is achieved is also very gentle. The result is that the yarn features less instances of damage on its surface, and also lower yarn/ceramic friction values than conventionally manufactured yarn. This means that this yarn can be used to advantage in further processing stages.
It was found, surprisingly, that yarn manufactured with the device according to the invention featured entirely closed cohesion of the thread in the water bath, which exhibited no apertures, or practically none, over the entire length of the thread. By contrast, yarns manufactured in the conventional manner feature constrictions in the water bath at intervals of 6 to 8 cm. In between, the thread opens out in balloon fashion into the individual filaments of the thread. Good thread cohesion, such as can be achieved with the device according to the invention, is of great advantage to further processing.
As was further found, surprisingly, the intermingling and cohesion of the thread, created with the device according to the invention, is extraordinarily stable under tension. Accordingly, the decrease in the number of knots per length unit, with increasing tensile stress, at least up to a specific thread tensile strength of 0.5 cN/dtex is at least one order of magnitude (one power of ten) less than with otherwise comparable filament yarns according to the prior art. The specific thread tensile strength mentioned, of 0.5 cN/dtex, corresponds approximately to the loading such as occurs, for example, at weft insertion in a loom, and therefore to a loading such as a thread experiences at the most in usual practice. The object of the present invention is, to this extent, also an entangled filament yarn, in which, as a characteristic feature according to Patent claim 16, the number of knots per unit length decreases up to a specific thread tensile strength of 0.5 cN/dtex by not more than 50%, but in particular by not more than 30%.
This extraordinarily high intermingling stability of the filament yarn according to the invention has a particularly advantageous effect on the degree of efficiency in the weaving mill preparation stage. Fewer shutdowns occur in that case with warping or beaming, and less waste material is generated. This also results in a mill run which is overall freer of operational problems.
In as much as the treatment chamber with the device according to the invention is capable of being filled with a gas at an essentially static overpressure and increased temperature, the gas is to advantage subjected to this pressure and this temperature throughout its entire passage through the treatment chamber, which on the one hand results in a better relaxation. On the other hand, the operational window is also substantially expanded, since an adequate relaxation is already possible at low pressures in the treatment chamber. In respect of thermosetting adjustment, a favourable dependency between the pressure applied and the duration of processing has been demonstrated, with the result that a desired shrinkage is even capable of being specifically adjusted.
For preference, the intake and/or outlet apertures of the treatment chamber are designed as nozzles closely encompassing the yarn, while the treatment chamber features a substantially larger cross-section in relation to them. This facilitates the creation of a largely static overpressure in the treatment chamber, and also reduces the emergence of treatment gas, which has a favourable effect on its consumption. In comparison with conventional intermingling nozzles, for example, this can be reduced to only about ⅓ to xc2xc. The intermingling effect is not impaired as a result, but is, on the contrary, enhanced.
The cross-section of the intake and/or outlet aperture is, in addition, for preference rectangular, as a result of which the filaments of the yarn, when running through the treatment chamber, are drawn apart to form a flat strip. In this form, they offer a larger surface area to the gas in the treatment chamber, and are more effectively heated by it.
Due to the expansion of the treatment chamber in the direction of run of the yarn (mostly vertical), it is a simple matter to influence the temporal length of treatment. In order to achieve an adequately long period even at higher operational speeds, it is preferable if the expansion of the treatment chamber is substantially greater between its intake and outlet aperture than its width (mostly horizontal) between them.
According to a further preferred embodiment, the treatment chamber features a feed aperture for the treatment gas, the cross-section of which is substantially greater than the cross-section of its intake and/or outlet apertures. This ensures that the gas will not be relaxed as soon as it flows into the treatment chamber, as is the case with conventional intermingling chambers, and accordingly impinges on the yarn as a jet, at a high speed. Rather, a uniform flooding of the treatment chamber, and the formation of a largely static pressure in it, is achieved. The pressure of the treatment gas does not essentially start to relax until it flows out through the intake and/or the outlet aperture.
Following the aforegoing, it can be understood that the treatment chamber, apart from its intake and outlet apertures and the feed aperture for the treatment gas, should as far as possible be completed closed.
It can further be understood that, as a material for the manufacture of the treatment chamber, metal or ceramics can be considered, the latter due to its favourable abrasion-resistant properties. Naturally, a metal provided with an abrasion-resistant coating would also be suitable.
The device according to the invention is used to advantage in a melt spinning system with a spin drawing and/or preliminary drawing line, as well as a winding-up device for the yarn between these two positions. At high spinning speeds in particular, in the range from 75 m/s, it is preferable in this situation if no means are provided in the drawing line for the heating of the yarn, since the effectiveness of the device according to the invention in particular with regard to the relaxing effect and thermosetting is higher without such pre-heating of the yarn. The device according to the invention may also be arranged, in the system referred to, immediately in front of the winding-up station; i.e. no further treatment of the yarn is required, nor does any extra time need to be accorded for possible further shortening, making use of an additional run way.
The device according to the invention is operated for preference with steam, and for preference with water vapour, as the treatment gas, and should be designed with an absolute pressure of up to about 10 bar for this.
The device according to the invention can be used for the entire titre range, i.e. from microfilament yarns through light titres and up to texture yarns, and BCF yarns (carpet yarns) in particular, as well as technical yarns.